The requirement of a functional DNA replication complex for a single-stranded DNA binding protein will be examined. Bacteriophage T7 will be used as a model system since its genomic sequence is known and the products of most of its genes have been identified. Most important is the wealth of biochemical information available on the proteins necessary for T7 DNA replication. This research will focus on the absolute requirement of T7 DNA replication and phage growth for the product of T7 gene 2.5 (gp2.5), a single-stranded DNA binding protein. T7 DNA replication is performed by a complex consisting of the product of gene 5, a DNA polymerase, the product of gene 4, a DNA helicase/primase, gp2.5, and a host protein, Escherechia coli thioredoxin, a processivity factor. While some protein-protein interactions between gp2.5 and other DNA replication proteins have been characterized, the necessity of gp2.5 for DNA replication and ultimately, phage viability, has yet to be determined.